Examples of an engine mounted in a vehicle include a port injection engine in which fuel is injected from an injector into an intake passage or an intake port, and an in-cylinder direct injection engine in which fuel is directly injected from an injector into a cylinder (into a combustion chamber). Also, there is known a so-called dual injection type of engine including an injector for in-cylinder injection that injects fuel into a cylinder (into a combustion chamber), and an injector for intake port injection that injects fuel into an intake passage or an intake port.
In an engine mounted in a vehicle, blow-by gas (an uncombusted mixture of air and fuel, and combustion gas) leaks from a combustion chamber into a crankcase through a gap between a piston and the wall surface of a cylinder. Blow-by gas cannot be expelled into the atmosphere due to containing a large amount of hydrocarbons (HC), oil components (engine oil mist), and the like. For this reason, the engine is equipped with a blow-by gas reducing device (PCV (Positive Crankcase Ventilation) device) that returns blow-by gas that has leaked into the crankcase back to an intake passage through a blow-by gas passage (e.g., see Patent Literature 1).
Meanwhile, a catalyst (e.g., a three-way catalyst) that removes hazardous components (HC, CO, NOx, and the like) contained in exhaust gas discharged from a combustion chamber is disposed in an exhaust passage of an engine, and catalyst warm-up control for raising the temperature of the catalyst early is performed. For example, in a vehicle in which an in-cylinder direct injection gasoline engine (or a dual injection type of engine) is mounted, the temperature of exhaust gas discharged from a combustion chamber is raised by setting the fuel injection timing to the latter stage of the compression stroke to cause the combustion state to be stratified combustion (or weak stratified combustion), and furthermore retarding the ignition timing of ignition by a spark plug, thus accelerating the warm-up of the catalyst (e.g., see Patent Literature 2 and 3).